1. Field of the Invention
This invention relates to a dampening water feeding method and a printing machine.
2. Description of the Related Art
In a printing machine, the feed rate of dampening water, as does the feed rate of ink, has a decisive influence on printing results. It is therefore necessary for the printing machine to adjust the feed rate of dampening water as well as the feed rate of ink properly.
To execute a method of automatically detecting the quantity of dampening water and controlling the feed rate thereof, an apparatus has been proposed that measures a film thickness of water on a roller by using an infrared sensor, for example. However, such an apparatus has difficulties in coping with environmental changes occurring in time of printing, and the apparatus itself is extremely expensive.
Then, in Japanese Unexamined Patent Publication No. 2002-355950, Applicants herein have proposed a method of controlling feeding rates of dampening water and ink in a printing machine by using first and second detecting patches presenting a difference in density variations after printing with varied feed rates of damping water and ink. The method of controlling feeding rates of dampening water and ink in a printing machine described in the above publication is capable of adjusting the feed rates of dampening water and ink properly.
A feed rate of dampening water required when starting a printing operation is dependent on the printing environment existent at that time. In practice, therefore, when starting a printing operation, the operator adjusts a feed rate of dampening water determined beforehand by computation, according to the printing environment occurring at that time. However, the experience of the operator may not be adequate to set a proper feed rate of dampening water easily at start of a printing operation, and may use a wasteful amount of printing paper.